Execution of catalytic conversions in the presence of ferrous metals



Patented Jan. 6, 1942 EXECUTION OF CATALYTIC CONVERSIONS IN THE PRESENCEOF FERROUS MET ALS George E. Liedholm and Robert M. Cole, Long Beach,and Irving I. Shultz, Los Angeles, Calil'., assignors to ShellDevelopment Company, San Francisco, Calif., a corporation of Delaware NoDrawing. Application September 9,1940,

Serial No. 356,036

ll Claims.

The present invention relates to the catalytic conversion of organicmaterials in the vapor phase at elevated temperatures in the presence offerrous metals. A particular aspect of the invention relates to thetreatment of hydrocarbon vapors at elevated temperatures, 1. e.- fromabout 500 F. to 1300" F., with dehydrogenation catalysts such, inparticular, as those comprising an oxide of chromium,. molybdenum,tungsten, va-

nadium, or manganese which are normally substantially free of iron andwhich are subject to poisoning by iron.

As is well known, one of the most practical and common methods forexecuting catalytic conversions of organic materials in the vapor phaseis to provide a porousbed of catalyst in a suitable reaction tube,converter or catalyst case,

and to pass the vapors of the carbonaceous reactant therethrough underappropriate conditions of temperature, pressure, etc. In most cases whentreating carbonaceous materials at temperatures of the order of 500 F.to 1300 F., the catalyst gradually loses its activity due to thedeposition thereon of carbon' and tarry materials. This deactivation ofthe catalyst is temporary and may be indefinitely counteracted byperiodically burning off the deposited materials in situ.

Many of the most effective catalysts for these various conversions aresusceptible to poisoning by iron. These various catalysts, when used forthe vapor phase conversion of organic materials at these elevatedtemperatures in theppresence of iron, steel or ferrous alloys, besidesundergoing the above-mentioned temporary deactivation due toaccumulation of carbon and tarry deposits,-

undergo a permanent deactivation due to an accumulation of iron or ironcompounds formed by the oxidation or corrosion of the ferrous metal incontact therewith. Even traces of iron derived from various parts of theplant, such as preheating coils, etc., carried with the reactant vaporsare often sufficient to cause a serious poisoning of-these catalysts.Thus,- as a general rule, it is found that the activity of thesecatalysts is decreased approximately linearly from 80% of their initialactivity with an iron content of 0.7% to 40% when the iron content isincreased to 1.3%. This deactivation of the catalyst, unlike that duetothe deposition of tarry materials, is permanent and cannot becounteracted by any ofv the known regeneration processes. Since thesevarious conversions are often executed under pressure and since,furthermore, they generally require the introduction or withdrawal ofconsiderablequantities of heat, usually through the confining walls ofthe reaction zone,

it is usually impractical in these processes to employ. apparatusconstructed of or lined with nonferrous materials such as silicon,ceramic materials, and the like,"and the use of iron, steel or ferrousalloy equipment 'is practically unavoidable.

The industry has-searched diligently for some practical method wherebythe transfer of iron tothese catalysts could be avoided, while at thesame time utilizing apparatus fabricated from ferrous metals. It has,for example, been proposed to employ apparatus plated with chromium,aluminum, copper, etc. Such apparatus sometimes works well for a' shorttime. It is found,

' however, that these various linings invariably have minute pin holesor become scratched by the, catalyst, and after a short period ofoperation the under-metal is attackedthrough these imperfections withthe result that the lining becomes pitted or peels, and iron istransferred to the catalyst. The contamination of these catasatisfactoryfor the purpose.

lysts by iron has also been minimized to a considerable extent by theuse of certain alloy steels such, in particular, as the more or lesscorrosionresistant steels containing chromium, molybdenum, vanadium,titanium, etc. It is found, for example, that whereas iron and plaincarbon steels are practically useless, the tendency to contaminate thecatalyst with iron is considerably decreased by the incorporation ofchromium. However, even chrome steel containing 27% chromium, which isthe highest chrome steel that can be fabricated, has not proven entirelyThe reaction vessels fabricated from this material are both expensiveand short-lived. After a relatively short period of use, they suddenlybegin to contaminate the catalyst with iron and must be discarded. Ithas also been proposed to employ ferrous metals pretreated with hydrogensulfide. This pretreatment is sometimes effective in preventing carbonformation in non-catalytic processes and when employing catalysts whichare not susceptible to iron poisoning. It does not, however, avoid ordecrease iron contamination and, in fact, increases it.

We have now found a simple, practical and effective method whereby thecontamination of these catalysts with iron, when used in such processesin contact with ferrous metals, may be substantially obviated. By theuse of our method these processes may be executed in apparatusconstructed of the more common,less expensive steels and ferrous alloyssuch as the common KA2, KA2S, KA2M0T, KA2Cb, KA2M0, and KAZST steels,while at the same time avoiding all substantial contamination of thecatalyst by iron. According to the method of our invention, this iseffected by maintaining certain specific concentrations of sulfurcompounds in the reaction zone.

It is generally known that when treating organic vapors at theseelevated temperatures with these catalysts in the presence of ferrousmetals in .the absence of any substantial amount of sulfur, corrosion ofthe ferrous metal and iron poisoning of the catalyst takes place. It isalso generally known that the corrosion and iron poisoning are usuallyincreased by the presence of sulfur in the feed. We have found bycareful investigation, however, that the types and characters of thecorrosions occurring with sulfurfree feeds and with sulfur-bearing feedsare different and that there is a region corresponding approximately tothe transition of one type of corrosion to the other where corrosion ofthe ferrous metal and iron transfer to the catalyst are practicallynegligible. This region where corrosion and iron transfer practically donot take place corresponds to a low, specific and narthere was addedsuflicient carbonyl sulfide to raise the sulfur content to 0.006%. Thismaterial was treated under the conditions described above for 200process cycles. During this time the conversion to propylene declinedfrom 33.5%

Example IV A similar set'of experiments was made in whichdimethylsulfide was added to the propane to prorow range of sulfurconcentrations. If the concentration of sulfur is increased beyond thisrange corrosion is greatly increased and large quantities of. iron aretransferred to the catalyst, and on the other hand, if the concentrationof sulfur is reduced beyond this range, corrosion of the other type andiron transfer are again increased.

The existence of this region of minimum iron transfer to the catalystmay be easily seen from the following illustrative examples. Theseexamples, for the sake of comparison, all relate to the dehydrogenationof propane vapors at a temperature of 1140 F. at a space velocity of -35per Propane vapors stubstantially free of sulfur were treated under theabove-described conditions. During only about 1 8 (and 38) processcycles the catalyst became contaminated with about 0.26% (and 0.35%)iron. In other words, in check runs during 19 and 38 process periodsiron was transferred from the KAZS steel reacwas, in general, betweenabout 0.0002% and 0.05%. Preferred limits of sulfur concentrations forindividual types of sulfur compounds were found to be:

. COS 00006-0015 RSR 0.005 -0.015

RSH 00005-0003 S03 0.002 0.015 SO: 0.002 -0.015 CS: 0.002 -0.008 HzS0.002 -0.008 Thiophene 0.002 -0.015

tion tube to the catalyst to the extent of about 0.24% (and 0.35%) byweight of the catalyst. It is thus seen that in the absence of sulfur,contamination of the catalyst by iron is considerable.

Example II A commercial propane fraction containing 0.0002% sulfur(principally as mercaptans) was treated under the above-describedconditions.

During about 120 (and 250) process cycles the' Example III vide thedesired sulfur content. The following iron contents of the catalystafter 200 process cycles were found:

Sulfur Iron in in feed catalyst Percent Percent While the contaminationof the catalyst by iron may be avoided by the presence of appropriateconcentrations of sulfur compounds generally, we have found that alltypes of sulfur compounds are not equally effective. The most preferredsulfur compound is carbonyl sulfide. This compound is considerably moreeffective than any of the others tested. Slightly less preferred butstill very effective are sulfur trioxide, thiophenic sulfur compounds,and dialkyl suliides. considerably less effective than these are themercaptans, sulfur dioxide, carbon disulflde, and hydrogen sulfide.Surprisingly enough, hydrogen sulfide was the least effective of allsulfur compounds tested. Thus, when treating propane containing hydrogensulfideunder the above-described conditions with the optimumconcentration of hydrogen sulfide (corresponding to 0.003% sulfur) theiron content of the catalyst after 200 process cycles was 0.11%.Comparing this figure with that shown in Example I, it is seen thathydrogen sulfide is effective. Comparing it with To a commercialsulfur-free propane fraction Example III, however, it is seen that it isnot I sten oxide, and alumina.

nearly as effective as carbonyl sulfide. According to a preferredembodiment of the invention,

therefore, a reducible sulfur compound, 1-. e. a

compound other than hydrogen sulfide, is ,em-

pounds, arsine, phosphine and the like, function in the same manner asthe sulfur compounds, although usually to a lesser extent. Since thesulfur compounds are the most efficient and most practical compounds touse these other metalloid compounds are of much less practical interest.The process of the present invention is generally applicable in theconversion of organic or carbonaceous materials in the vapor phase atelevated temperatures at least equal to 500 F. wherein the conversion isexecuted in ferrous metal equipmentwith the aid of catalysts which areaffected by contamination with iron. It is particularly advantageous inall such processes where the catalyst is periodically regenerated insitu by burning 01f deposited tarry materials bonyl sulfide. Thiscompound and, to a lesser extent, dialkyl sulfides and sulfur trioxidesare,

much less prone to cause sulfur poisoning than are, for example, sulfurdioxide, mercaptans, carbon dlsulfide, etc., and are infinitely lesstoxic than hydrogen sulfide. In fact, the reason why carbonyl sulfide,dialkyl sulfides and sulfur trisince in these processes the tendency foriron contamination is more pronounced. The pres-- ent process is alsomost advantageous for such of these processes as are endothermic sincein these processes the metal confining walls are usually heated, andthis likewise increases the tendency for the catalyst to becomecontaminated by iron. Particular processes for which the present processis exceptionally well suited are, for example, the dehydrogenation ofhydrocarbons such, for instance, as the, catalytic dehydrogenation ofpropane, butane, pentane, cyclohexane, etc., to the correspondingolefines and/or atures above about 500 F. with organic vapors and areaffected by contamination by iron. As

, examples of such catalysts there may be mentioned by way ofillustration the many catalysts comprising one or more of the metals,Ti, Zr, Ce, Th, V, Nb, Ta, Cr, Mo, .W, U, and Mn, or the oxides thereof.These catalysts often contain minor percentages of these metals or com-'in order to secure the advantages of the present pounds thereof such,for example, as the molybdates, tungstates, chromates, chromites,manganates, etc., in combination with major amounts of relatively inertmaterials such, for example, as alumina, magnesia, zirconia, fullersearth, zeolites, permutites, active carbon, etc. They are usuallysubstantially freeof iron, cobalt and nickel. A preferred group ofcatalysts'is, for example, the dehydrogenation catalysts such, forinstance, as those' comprising chromium oxide, and/or molybdenum oxide,and/or tung- These catalysts are exceptionally suitable for thedehydrogenation of hydrocarbons, the reforming of gasolines and thecyclization of aliphatic hydrocarbons, but sufferconsiderably from ironcontamination when employed in ferrousmetal equipment. Certain of theabove-mentioned catalysts, it is known, are susceptible to poisoning bysulfur. It is found, however, that these catalysts are usuallysubstantially unaffected by the small concentrations of sulfur compoundsemployed in the process of the invention. when the sulfur compound,according to the pres ent invention, is employed in the form of'caroxideare less toxic is believed to be due to the fact that they are notconverted in the process'to any substantial extent to hydrogen sulfide,whereas mercaptans, carbon disulflde, etc., are often converted largelyto hydrogen sulfide.

The contamination of the catalyst by iron in the execution of thesevarious reactions may be inhibited, according to the present process, in

the presence of any of the steels and common ferrous alloys. Iron andmild steel are not usually employed in these processes due to theirinability to withstand the more or less severe reaction conditions.Particularly suitable materials which may be used to considerableadvantage, according to the present invention, are the chrome steelssuch as KAZ, KA2S, KA2ST, KA2Cb, KA2Mo, KA2MoT, etc. In the past theseotherwise excellent steels have not been found entirely suitable due totheir tendency to cause iron contamination of the catalyst after a shortperiod of use, and the industry has been forced to go to the veryexpensive and difliculty workable high-chrome steels such as 27 Cr, etc.These latter materials, although definitely superior to most low-chromesteels, are nevertheless far from satisfactory and cause ironcontamination after a relatively short period of time. When thesematerials are used, according to the process of the present invention,any of these steels may be employed indefinitely without any appreciabletendency to cause iron contamination.

Many of the organic materials serving as reactants in the processes inwhich the present invention may be employed normally contain small toappreciable amounts of sulfur. It will be appreciated in view of ,theabove, therefore, that method the sulfur content of these materials mustbe adjusted prior to treatment to within the narrow limits specifiedabove. In such cases where the sulfur content of the feed is normallytoo low', it is merely necessary to add the required amount of sulfur tobring it within the specified limits, In such cases where the sulfurcontent is too high, as is often the case when treating petroleumfractions, the excess sulfur should be removed. This may be done by anyof the conventional Also, besides adjusting the concentration of sulfurto within the desired limits, it is preferable to take intoconsideration the type of sulfur 1 compounds present. Mostsulfur-bearing'petro- This 'is especially true leum distillates containappreciable quantities of hydrogen sulfide and mercaptans. According toa preferred embodiment of the invention. less desirable sulfur compoundsare substantially removed and the correct amount of a preferred sulfurcompound, such as carbonyl sulfide, is

added.

Although the sulfur or sulfur compound may be added to the reaction zoneseparately from the feed or by any other convenient method, the mostconvenient and practical method for introducing the desired sulfur orsulfur compound is as a vapor mixedwith the reactant vapors. Thus, forinstance, a normally gaseous sulfur compound may be mixed with thepreheated reactant vapors entering the reaction zone or the sulfurcomdesulfurization. treatments.

about 0.007%

Example V This example illustrates the exceptional effectiveness ofcarbonyl sulfide sulfur in preventing iron poisoning of the catalyst andthe vast superiority of carbonyl sulfide sulfur over mercaptan sulfur.

A commercial propane fraction containing about 0.007% sulfur, of which0.0005% was mercaptan sulfur and the remainder was carbonyl sulfide, wastreated under the conditions described above for about 1000 processcycles. During this time the conversion to propylene declined from 32%to 26%.. The catalyst at the end of the 1000 process cycles analyzed0.047 iron (initial iron content 0.02(5) If the 0.0005 mercaptan sulfuris replaced by carbonyl sulfide sulfur, no increase in the ironcontamination of the catalyst takes place and the conversions areincreased about 7% of the above value.

Example VI 3. In a process for the conversion of carbonaceous materialsin the vapor phase at an elevated temperature at least equal to 750 F.wherein the reactant vapors are contacted with supported A commercialpropane fraction containing sulfur as carbonyl sulfide was treated witha 10% KOH solution in alcohol to reduce the sulfur concentration toabout 0.002%. This material was treated under the conditions describedabove for about 1000 process cycles. During this time the conversion topropylene declined from,33-34% to 27.5%. The catalyst at the end of the1000 process cycles analyzed 0.04% iron (initial iron content 0.02(5) Itis seen from this example that the presence of about 0.002% sulfur ascarbonyl sulfide is sufficient to substantially eliminate poisoning ofthe catalyst with iron.

The foregoing examples are submitted solely to illustrate the process ofthe invention and the advantageous results obtainable thereby, and arenot to be construed as limiting the invention.

We claim as our invention:

1. In a process for the conversion Qf carbonaceous materials in thevapor phase at an elevated temperature at least equal to 750 F. whereinthe reactant vapors are contacted with a catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in the feed to thereaction zone from 0.0006% to 0.015% sulfur in the form of a volatileoxygenated sulfur compound.

2. In a process for the conversion of carbonaceous materials in thevapor phase in a chrome steel reactor at an elevated temperature atleast equal to 750 F. wherein the reactant vapors'are contacted with acatalyst susceptible to contamination by iron in the presence of aferrous metal and the catalyst is periodically regenerated in situ bythe oxidation of combustible deposits therefrom, the step of inhibitingthe contamina-' tion of the catalyst by iron which comprises maintainingin the feed to the reaction zone from 0.0006% to 0.015% sulfur intheform of a volatile oxygenated sulfur compound.

chromium oxide catalyst in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in the feed to thereaction zone from 0.0006% to 0.015% sulfur in the form of a volatileoxygenated sulfur compound.

4. In a process for dehydrogenating carbonaceous material in the vaporphase at an elevated temperature at least equal to 750 F. wherein thereactant vapors are contacted with a dehydrogenation catalystsusceptible to contaimination by iron in the presence of a ferrous metaland the catalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in thefeed to thereaction zone from 0.0006% to 0.015% sulfur in the form of a volatileoxygenated sulfur compound.

5. In a process for the dehydrogenation of butane in the vapor phase atan elevated temperature at least equal to 750 F. wherein butane vaporsare contacted with a dehydrogenation. catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in the feed to thereaction zone from 0.0006% to 0.015% sulfur in the form of a volatileoxygenated sulfur compound.

6. In a process for the dehydrogenation of propane in the vapor phase atan elevated temperature at least equal to 750 F. wherein propane vaporsare contacted with a dehydrogenation catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof' the catalyst by iron which comprises maintaining in the feed to thereaction zone from 0.0006% to 0.015% sulfur in the form of a volatileoxygenated sulfur compound.

7. In a process for the catalytic reforming of a petroleum distillatewherein distillate vapors are contacted with a catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in the feed to thereaction zone from 0.0006% to 0.015% sulfur in the form of a volatileoxygenated sulfur compound.

8. In a process for the conversion of carbonaceous materials "in thevapor phase at an elevated temperature at least equal to 750 F. whereinthe reactant vapors are contacted with a catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in the feed to thereaction zone a quantity of carbonyl sulfide equivalent to from 0.0006%to 0.015% sulfur.

9. In a process for the conversion of carbonaceous materials in thevapor phase at an elevated temperature at least equal to 750 F.

wherein the reactant vapors are contacted with a catalyst susceptible tocontaminationby iron in the presence of a ferrous metal and the catalystis periodically regenerated in situ by the oxidation of combustibledeposits therefrom, the step of inhibiting the contamination of thecatalyst by iron which comprises maintaining in the feed to the reactionzone a quantity of sulfur trioxide equivalent to from 0.0006% to 0.015%sulfur.

10. In a process for the catalytic treatment of a petroleum hydrocarbonat an elevated temperature at least equal to 750 F. wherein thehydrocarbon vapor is contacted with a catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationofthe catalyst by iron which comprises pretreating the hydrocarbon feedto remove any'hydrogen sulfide present and then adjusting the sulfurcontent of the feed to from 0.0006% to 0.015% by the addition of avolatile oxygenated sulfur compound.

11. In a process for-the dehydrogenation of butane in the vapor phase atan elevated temperature at least equal to 750 F. wherein the reactantvapors are contacted with a dehydrogenation catalyst susceptible tocontamination by iron in the presence of a ferrous metal and thecatalyst is periodically regenerated in situ by the oxidation ofcombustible deposits therefrom, the step of inhibiting the contaminationof the catalyst by iron which comprises maintaining in the feed to thereaction zone a quantity of-carbonyl sulfide equivalent to from 0.0006%to 0.015% sulfur.

GEORGE E. LIEDHOLM.

ROBERT M. COLE. IRVING I. SHULTZ.

